Boys who are short at birth have double the risk of attempting suicide as adults even if their growth "catches up" in childhood, a study suggests.

Those under 47cm (18.5 inches) were found to be at highest risk.

The Journal of Epidemiology and Community Health says poor foetal growth may have long-term effects on brain chemistry.

The Swedish researchers said more should be done to help pregnant women and babies who were at risk.

Violent suicides

Researchers from the Karolinska Institute in Stockholm looked at national data on male births between 1973 and 1980 and at suicide attempts up until 1999.

The shortest babies were compared to those with an average length of 50-51cm (19.6 to 20 inches).

Any research that throws light on the reasons why some people are more vulnerable than others is essential

Margorie Wallace, Sane

There were 759 violent suicide attempts - defined as hanging, using a gun or a knife jumping from heights or in front of a vehicle or drowning, amongst the whole group.

The link between birth length and suicide risk was strongest, but a birthweight of under 2,500g (5.5lbs) was also linked to an increasing risk of suicide attempts.

The study also found men who were normal length babies, but who were short in adult life, were 56 per cent more likely than tall men to attempt to take their own lives.

Drug misuse

Low levels of the brain chemical serotonin, which have been linked to aggression and suicidal behaviour could be the key, the researchers say.

Dr Ellenor Mittendorfer-Rutz, who led the study, said it was possible poor growth in the womb - caused by maternal drug or alcohol use or a poor diet - affected both birth length and how the baby's brain processed serotonin.

Both were determined during the second trimester, she suggested.

Dr Mittendorfer-Rutz said more should be done to help pregnant women and babies.

"It is possible to identify at-risk pregnancies and mothers who are in adverse situations, such as those with psycho-social problems, teenage mothers and those with a criminal record.

"There is already some evidence to show intervening with these mothers can have an effect on the child's long-term outcome.

"We could also think about better pre-natal care for the mothers."

Marjorie Wallace, chief executive of mental health charity Sane, said: "We believe that when someone's mental and emotional fragility leads them to take their own life, the causes are like all conditions partly genetic and partly environmental, a mix of inner and outer stresses.

"Any research that throws light on the reasons why some people are more vulnerable than others is essential.

"With suicide rates, particularly among young men, still at a disturbingly high level, research of this kind is urgent to prevent the often unnecessary loss of life."